Laser-assisted cleaving of a reconstituted wafer for stacked die assemblies

ABSTRACT

A method of forming stacked die devices includes attaching first semiconductor die onto a wafer to form a reconstituted wafer, and then bonding second semiconductor die onto the first semiconductor die to form a plurality of singulated stacked die devices on the wafer. A support tape is attached to a bottomside of the second semiconductor die. A dicing tape is attached to the wafer. The wafer is laser irradiated before or after attachment of the dicing tape at intended dicing lanes that align with gaps between the first semiconductor die to mechanically weaken the wafer at the intended dicing lanes, but not cut through the wafer. The dicing tape is pulled to cleave the wafer into a plurality of singulated portions to form a plurality of singulated stacked die devices attached to the singulated wafer portions by the dicing tape. The support tape is removed prior to cleaving.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of and claims priority to U.S. patentapplication Ser. No. 13/197,856, filed on Aug. 8, 2011, now U.S. Pat.No. 8,575,758.

FIELD

Disclosed embodiments relate to stacked die assembly methods thatutilize reconstituted wafers.

BACKGROUND

Conventional stacked die assembly methods involve die-to-die (D2D)assembly when the top die extends beyond the perimeter or boundary(e.g., area) of the bottom die. Die-to-wafer (D2W) assembly, however, ispreferable to D2D for cost reasons. One option to enable D2W assemblyfor such die stacks is to space out the lower die on the semiconductorwafer to allow D2W bonding. However, the large gaps between the lowerdie results in a loss of otherwise available die area. Another D2Woption involves creating a “reconstituted wafer” formed by bonding thesmaller die to a carrier wafer to achieve the needed spacing prior tobonding the top die thereon.

SUMMARY

Disclosed embodiments recognize that using conventional mechanicaldicing operations for forming stacked die assemblies using thereconstituted wafer method, as the dicing blade comes in close proximityto the periphery bond pads on the top semiconductor die, adebris-comprising slurry can be deposited thereon. The debris-comprisingslurry can damage or contaminate exposed periphery pads which canprevent reliable wirebonding thereto. Damage and contamination ofperiphery bond pads on the top semiconductor die has been found to bemore problematic when the first semiconductor die is relatively thin(e.g., <120 μm) and the gap between die is small (e.g., <25 μm).

Disclosed embodiments include laser-assisted cleaving of a reconstitutedwafer for forming stacked die assemblies that singulate the stacked diewithout damaging or contaminating the periphery bond pads of the topdie. One disclosed embodiment is a method of forming stacked die devicesthat includes attaching a plurality of first semiconductor die onto asurface of a wafer to form a reconstituted wafer, and then bonding aplurality of second semiconductor die with their topside down onto theplurality of first semiconductor die to form a plurality of singulatedstacked die devices attached to the wafer. The wafer can comprise acarrier wafer or a wafer including a plurality of interposer die. Asupport tape is attached to a bottomside of the plurality of secondsemiconductor die.

A laser is used to irradiate the carrier wafer at intended dicinglocations that align with gaps between the plurality of firstsemiconductor die under conditions that mechanically weaken the wafer,but does not cut through the intended dicing lanes. A dicing tape isapplied either before or after laser irradiating. The dicing tape ispulled resulting in cleaving (separation of) the wafer along theintended dicing lanes into a plurality of singulated portions. Thesupport tape is removed prior to cleaving, which generally occurs whilepulling/stretching the dicing tape. Each singulated portion is attachedto the dicing tape and includes one of the plurality of singulatedstacked die devices on a wafer portion. The singulated stacked diedevices can then be removed from the dicing tape and, in one exampleembodiment, attached to a package substrate such as a lead frame,followed by wire bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart that shows steps in an example method for formingstacked die devices including laser-assisted cleaving of a reconstitutedwafer, according to an example embodiment.

FIG. 2A is a cross sectional depiction of the arrangement followingattaching a plurality of first semiconductor die onto a surface of awafer to form a reconstituted wafer according to an example embodiment.

FIG. 2B is a cross sectional depiction of the arrangement having secondsemiconductor die bonded topside down onto first semiconductor die toform a plurality of stacked die devices on the carrier wafer, accordingto an example embodiment.

FIG. 2C is a cross sectional depiction of the arrangement followingattaching a support tape to a bottomside of the plurality of secondsemiconductor die, according to an example embodiment.

FIG. 2D is a cross sectional depiction of the resulting arrangementfollowing laser irradiating step for the embodiment where dicing tape isapplied to the wafer after laser irradiating.

FIG. 2E is a cross sectional depiction of the resulting arrangementfollowing attachment of the dicing tape after laser irradiating,according to an example embodiment.

FIG. 2F is a cross sectional depiction of the arrangement followingpulling the dicing tape to cleave the wafer along the intended dicinglanes into a plurality of singulated portions that shows a carrier wafersevered along the dicing lanes into a plurality of carrier portions thateach remain attached to the dicing tape, according to an exampleembodiment.

FIG. 3A is a cross sectional depiction showing the arrangement resultingafter flipping the arrangement shown in FIG. 2C and attaching a dicingtape to the carrier wafer, for an alternate embodiment where the dicingtape is applied before laser irradiating, according to an exampleembodiment.

FIG. 3B is a cross sectional depiction showing the arrangement resultingafter laser irradiating through the dicing tape, according to an exampleembodiment.

FIG. 3C is a cross sectional depiction showing the arrangement resultingafter pulling the dicing tape to cleave the carrier wafer along theintended dicing lanes into a plurality of singulated portions thatcomprise carrier portions each having a stacked device thereon thatremains attached to the dicing tape, according to an example embodiment.

FIG. 4 is a cross sectional view of an example stacked die device formedby a disclosed method including laser-assisted cleaving of areconstituted wafer, where the wafer comprises an interposer, accordingto an example embodiment.

FIGS. 5A and 5B are scanned images of the edge of a silicon diefollowing disclosed laser-assisted cleaving showing characteristic microcracks following a 1-pass and a 2-pass laser irradiation process,respectively, according to an example embodiment.

DETAILED DESCRIPTION

Example embodiments are described with reference to the drawings,wherein like reference numerals are used to designate similar orequivalent elements. Illustrated ordering of acts or events should notbe considered as limiting, as some acts or events may occur in differentorder and/or concurrently with other acts or events. Furthermore, someillustrated acts or events may not be required to implement amethodology in accordance with this disclosure.

Disclosed embodiments include laser-assisted cleaving of a reconstitutedwafer for forming stacked die assemblies where the singulating of thestacked die does not damage or contaminate the exposed periphery pads onthe top die. Disclosed embodiments also include stacked die devices thatcomprise an interposer die (e.g., silicon or quartz interposer)including a plurality of through substrate vias (TSVs), and a die stackattached to the interposer. The die stack includes a secondsemiconductor die bonded with its topside down onto a firstsemiconductor die. The edges of the interposer die include laser damagedregions including micro cracks.

FIG. 1 is a flow chart that shows steps in an example method 100 forforming stacked die devices including laser-assisted cleaving of areconstituted wafer, according to an example embodiment. Step 101comprises attaching a plurality of first semiconductor die onto asurface of a wafer to form a reconstituted wafer. The firstsemiconductor die can include a plurality of TSVs. The wafer cancomprise a silicon carrier wafer or a glass carrier wafer, such asquartz glass, silica glass or a tempered soda-lime glass such as PYREX®.In another embodiment the wafer comprises a plurality of interposer die,such as silicon or glass interposer die that include TSVs.

FIG. 2A is a cross sectional depiction of the arrangement 200 followingstep 101 that shows a reconstituted wafer comprising a plurality offirst semiconductor die 222 attached to a surface of a wafer 210 shownas a carrier wafer 210. Although wafer 210 is shown as a carrier waferin FIGS. 2A-2F, in other embodiments wafer 210 comprises a plurality ofinterposer die, such as interposer die including TSVs. Although notshown, the bottomside of first die 222 (side having protruding TSV tips217(a)) includes a dielectric layer lateral to the TSV tips 217(a).

The carrier wafer 210 is generally 280 to 750 μm thick. The firstsemiconductor die 222 can be seen to include TSVs 217 includingprotruding TSV tips 217(a). A permanent or temporary adhesive (e.g., anepoxy) 206 secures the first semiconductor die 222 to the carrier wafer210.

Step 102 comprises bonding a plurality of second semiconductor die withtheir topside down onto the plurality of first semiconductor die to forma plurality of stacked die devices on the wafer 210. The secondsemiconductor die can extend beyond the perimeter or boundary of thefirst semiconductor die and the topside of the second semiconductor diecan include bond pads in this extended region for the stacked diedevices. Thermo-compression (TC) bonding is one example bonding methodthat may be used in step 102.

“Extend beyond the perimeter or boundary of the first semiconductor die”includes the case the second semiconductor die is larger in area ascompared to the first semiconductor die, as well as other arrangements.For example, in a first arrangement the second semiconductor die can berectangular and smaller in area as compared to the first semiconductordie, but has two sides that extend beyond the first semiconductor in onedimension. In a second arrangement, the second semiconductor die isoffset relative to the first semiconductor die such that some of the topsecond semiconductor die hangs over the first semiconductor die. Thissecond arrangement may be used, for example, on stacked memories, wherethe equal sized die are offset back and forth up the stack to allowaccess to periphery bond pads on the top die.

FIG. 2B is a cross sectional depiction of the arrangement 240 havingsecond semiconductor die 221 bonded topside down onto firstsemiconductor die 222 to form a plurality of stacked die devices 220 onthe carrier wafer 210. The second semiconductor die 221 is shown largerin width than the first semiconductor die 222, and the topside 226 ofthe second semiconductor die 221 includes bond pads 232 including someperiphery bond pads 232(a) that extend beyond an area of the firstsemiconductor die 222. The bottomside of the second semiconductor die isshown as 225. Underfill 227 is shown between the first semiconductor die222 and the second semiconductor die 221. Underfill 227 can be appliedbefore or after bonding the first semiconductor die 222 to the secondsemiconductor die 221 (step 102).

Step 103 comprises attaching a support tape 230 to a bottomside 225 ofthe plurality of second semiconductor die 221. As used herein, a“support tape” is defined broadly to include more than simply tapematerials so as to also include a wide variety of adhering arrangements,such as a support film that can be applied with a temporary adhesive toa semi-flexible support material. FIG. 2C is a cross sectional depictionof the arrangement 250 following step 103 comprising a plurality ofstacked die devices 220 comprising a second semiconductor die 221 bondedto first semiconductor die 222 on the wafer 210, with a support tape 230attached to the bottomside 225 of the plurality of second semiconductordie 221.

Step 104 comprises laser irradiating the carrier wafer 210 underconditions (e.g., power, focal length, time) to mechanically weaken thecarrier wafer 210 but not ablate or cut through intended dicing lanes211 in the carrier wafer that align with gaps between the plurality offirst semiconductor die 222, so that the carrier remains a single wholewafer following the laser irradiation. The laser irradiating conditionsincludes laser alignment selected so that the carrier wafer 210 isdamaged in the dicing lanes 211 just beyond (e.g., within 2 mm of) theperiphery of first semiconductor die 222, yet does not damageoverhanging regions of second semiconductor die 221. FIGS. 5A and 5Bdescribed below show scanned optical images of example silicon waferedges along a dicing lane 211 after disclosed laser irradiation andsubsequent cleaving.

FIG. 2D is a cross sectional depiction of the resulting arrangement 260following laser irradiating step 104 for the embodiment where the dicingtape is applied to the carrier wafer after laser irradiating. Dashes inthe carrier wafer 210 in the dicing lanes 211 are used to indicate laserinduced damage. As shown in FIG. 2D, the resulting arrangement 260 wasflipped 180 degrees to facilitate laser irradiating the carrier wafer210.

Step 105 comprises attaching a dicing tape 261 to the wafer 210 oppositethe stacked devices 220. Step 105 generally comprises applying thedicing tape along with a tape frame.

Attaching of the dicing tape can take place before or after laserirradiating (step 104). When the dicing tape 261 is applied before laserirradiating, since the laser irradiation is through the dicing tape, thedicing tape is selected so that it is transmissive to the wavelengthused for laser irradiating, which is typically an infrared (IR)wavelength, so that the dicing tape is selected to be IRtransmissive/transparent. FIG. 2E is a cross sectional depiction of theresulting arrangement 270 following attachment of the dicing tape 261for the embodiment the dicing tape is applied to the carrier wafer afterlaser irradiating.

Step 106 comprises pulling/stretching the dicing tape 261 to cleave thewafer along the intended dicing lanes 211 to form gaps 210(b), resultingin a plurality of singulated portions having stacked devices on waferportions that each remains attached to the dicing tape, according to anexample embodiment. A suitable machine can be used for pulling thedicing tape 261, such as commercially available separators, which aregenerally integrated together with the laser for laser irradiation (step104). The support tape 230 is removed prior to the cleaving/separation,which generally occurs while pulling/stretching the dicing tape 261.

FIG. 2F is a cross sectional depiction of the arrangement 280 followingpulling the dicing tape to cleave (separate) the carrier wafer 210 alongthe intended dicing lanes 211 to form gaps 210(b), resulting in aplurality of singulated portions 250 that comprise wafer portions shownas carrier portions 210(a) each having a stacked device 220 thereon thatremains attached to the dicing tape 261, according to an exampleembodiment. Unconnected carrier portions 210(c) between carrier portions210(a) can be seen in FIG. 2F that are formed when portions of thecarrier wafer that do not include stacked devices 220 are pulled in step106. Unconnected carrier portions 210(c) are discarded.

As described above, the dicing tape 261 can be applied before or afterlaser irradiating (step 104). FIGS. 3A-C show cross sectional depictionsof the resulting arrangements after steps for the alternate embodimentwhere the dicing tape 261 is applied before laser irradiating. In thisembodiment the dicing tape is transmissive to the wavelength of thelaser used for laser irradiation, typically an IR wavelength, so thatdicing tape in this embodiment can comprise an IR-transparent dicingtape 261.

FIG. 3A is a cross sectional depiction showing arrangement 310 resultingafter flipping arrangement 250 shown in FIG. 2C and attaching a dicingtape 261 to the carrier wafer 210. No dicing lanes 211 are shown in FIG.3A since this depiction is shown before laser irradiating. Arrangement310 is then laser irradiated through the dicing tape 261 in thisembodiment, with the resulting arrangement 320 shown in FIG. 3B. Sincethe dicing tape 261 is transmissive to the wavelength of the laser usedfor laser irradiation, laser damage in the dicing lanes 211 occurs,which is shown as dashes in the carrier. FIG. 3C is a cross sectionaldepiction showing the arrangement 330 resulting after pulling the dicingtape 261 to cleave the carrier wafer 210 along the intended dicing lanes211 to form gaps 210(b), resulting in a plurality of singulated portions250 that comprise carrier portions 210(a) each having a stacked device220 thereon, and unconnected carrier portions 201(c) that remainattached to the dicing tape 261, according to an example embodiment.Thus, the gaps 210(b) formed occur under the region of the secondsemiconductor die 221 that extends beyond the perimeter or boundary ofthe first semiconductor die 222. As described above, the support tape230 is removed prior to cleaving/separation, which generally occurswhile pulling/stretching the dicing tape 261.

As described above, the wafer can comprise a plurality of interposer diethat each includes a plurality of TSVs, where after pulling the dicingtape (step 106) the plurality of interposer die become part of theplurality of singulated portions. The interposer die can comprisesilicon interposer die, where after pulling/stretching the dicing tape,the edges of the interposer die for the plurality of singulated carrierportions include laser damaged regions that include micro cracks and aplurality of polysilicon crystallites. The wafer can also comprise aplurality of glass interposer die and wherein after the pulling edges ofthe plurality of singulated carrier portions include laser damagedregions that include a plurality of micro cracks.

Since disclosed methods eliminate the need for a conventional dicingblade needed for conventional stack die assembly, the periphery pads232(a) of the second semiconductor die 221 are at much lower risk ofbeing damaged or contaminated. As a result, disclosed methods improvewirebonding reliability to bond pads 232(a) on the second die forstacked die devices.

Disclosed laser-assisted cleaving can produce stacked die devices thathave certain distinguishable final features related to disclosedlaser-assisted cleaving processing. For example, FIG. 4 is a crosssectional depiction of an example stacked die device 400. Stacked diedevice 400 comprises an interposer die 310, shown as a siliconinterposer die 310 including a plurality of TSVs 317 with no activecircuitry, and a die stack 320 that comprises a second semiconductor die221 bonded to first semiconductor die 222 on the interposer die 310,wherein the second semiconductor die 221 is bonded with its topside 226down onto the first semiconductor die 222. Edges of the interposer die310 include laser damaged regions, such as shown in damage region inFIGS. 5A and 5B described below.

The second semiconductor die 221 can be seen to be larger in width ascompared to the first semiconductor die 222 and the topside 226 of thesecond semiconductor die 221 includes bond pads 232(a) that extendbeyond an area of the first semiconductor die 222. The firstsemiconductor die 222 includes a plurality of TSVs 217 having protrudingTSV tips 217(a). A redistribution layer (RDL) may be used to route fromTSVs 317 to pads that line up to TSV tips 217(a). Underfill 327 is shownbetween the interposer die 310 and the first semiconductor die 222.

FIGS. 5A and 5B are scanned optical images of the edge of a silicon diefrom a silicon wafer after disclosed laser-assisted cleaving showingmicro cracks following a 1-pass and a 2-pass laser process,respectively, according to an example embodiment. The die 510 shown inFIG. 5A is 60 μm thick, and laser induced micro-cracks can be seen inthe laser damaged region 520 shown. The die 540 shown in FIG. 5B is 75μm thick, and laser induced micro-cracks can be seen in the laserdamaged region 550 shown. Two (2) micro-crack regions indicative of thetwo passes of laser being focused at two different levels can be seen.The top region is much smaller in micro crack width vs. the lowerregion. Although the scanned images are shown for silicon substrates,glass substrates, such as for quartz interposers are expected to haveanalogous micro cracks resulting from disclosed laser-assisted cleaving.

Disclosed embodiments can be integrated into a variety of assembly flowsto form a variety of different stacked die devices and related products.The semiconductor die may include various elements therein and/or layersthereon, including barrier layers, dielectric layers, device structures,active elements and passive elements including source regions, drainregions, bit lines, bases, emitters, collectors, conductive lines,conductive vias, etc. Moreover, the semiconductor die can be formed froma variety of processes including bipolar, CMOS, BiCMOS and MEMS.

Those skilled in the art to which this disclosure relates willappreciate that many other embodiments and variations of embodiments arepossible within the scope of the claimed invention, and furtheradditions, deletions, substitutions and modifications may be made to thedescribed embodiments without departing from the scope of thisdisclosure. For example, the first semiconductor die 222, secondsemiconductor 221, or both the first semiconductor die 222 and secondsemiconductor 221 can be multi-die stacks.

We claim:
 1. A method of forming stacked die devices, comprising:attaching a plurality of first semiconductor die having plurality ofTSVs onto a surface of a wafer to form a reconstituted wafer; bonding aplurality of second semiconductor die each of said die having a topsidewith a plurality of bond pads thereon, wherein said plurality of secondsemiconductor die are bonded with their topside down onto said pluralityof first semiconductor die to form a plurality of singulated stacked diedevices attached to said wafer and wherein said plurality of TSVs onsaid first semiconductor die are bonded to a portion of said pluralityof bond pads of said second semiconductor; attaching a support tape to abottomside of said plurality of second semiconductor die; attaching adicing tape to said wafer; laser irradiating said wafer at intendeddicing lanes on said wafer that align with gaps between said pluralityof first semiconductor die to mechanically weaken but not cut throughsaid intended dicing lanes, and pulling said dicing tape to cleave saidwafer along said intended dicing lanes into a plurality of singulatedportions, wherein said plurality of singulated portions are attached tosaid dicing tape and each include one of said plurality of singulatedstacked die devices.
 2. The method of claim 1, wherein said dicing tapeis attached to said wafer after said laser irradiating.
 3. The method ofclaim 1, wherein said dicing tape is attached to said wafer before saidlaser irradiating, and said dicing tape is infrared (IR) transparent. 4.The method of claim 1, wherein said second semiconductor die extendsbeyond a perimeter or boundary of said first semiconductor die, andwherein said topside of said second semiconductor die includes bond padsthat extend beyond said perimeter or said boundary of said firstsemiconductor die.
 5. The method of claim 1, wherein said intendeddicing lanes are within 2 mm of said perimeter or said boundary of saidfirst semiconductor die.
 6. The method of claim 1, wherein said wafercomprises a silicon carrier wafer or a glass carrier wafer.
 7. Themethod of claim 1, wherein said first semiconductor die includes aplurality of through substrate vias (TSVs).
 8. The method of claim 1,wherein said wafer comprises a plurality of interposer die that eachincludes a plurality of through substrate vias (TSVs), and wherein aftersaid pulling said dicing tape said plurality of interposer die becomesingulated interposer die and part of said plurality of singulatedportions.
 9. The method of claim 8, wherein said wafer comprises aplurality of silicon interposer die and wherein after said pulling saiddicing tape edges of said singulated interposer die include laserdamaged regions that include micro cracks and a plurality of polysiliconcrystallites.
 10. The method of claim 8, wherein said wafer comprises aplurality of glass interposer die and wherein after said pulling saiddicing tape edges of said singulated interposer die include laserdamaged regions that include a plurality of micro cracks.
 11. The methodof claim 1, wherein said support tape is removed prior to cleaving saidwafer while said pulling of said dicing tape.